Numerical and Experimental Investigation of the Effect of Ultrasonic Acoustic-Field Orientation on Size-Dependent Aerosol Particle Redistribution

Ultrasonic acoustic agglomeration can enhance the removal of fine airborne particles, but the effect of acoustic-field orientation remains insufficiently understood. This study combines numerical and experimental analyses to evaluate how ultrasonic source orientation affects size-dependent particle migration and aerosol redistribution in a circular air duct. A three-dimensional multiphysics model based on the Gor’kov potential was used to calculate sound-pressure distributions and direction-dependent acoustic radiation forces. The predicted resonance behavior was compared with measurements from a fabricated prototype source operating at a resonance frequency of 49.35 kHz and generating a sound pressure level of 147 dB. Particle number concentrations were measured upstream and downstream at airflow velocities of 0.5 and 1.0 m/s, with and without mechanical particle dosing, for source orientations of 0°, 90°, and 180°. The numerical results showed that source orientation substantially redistributes the directional components of the acoustic radiation force. Experimentally, particle reduction increased with particle size. Under mechanical dosing, the mean reduction in the 5–10 μm fraction reached 40.05% at 180°, compared with 28.08% at 0° and 24.20% at 90°. However, these differences were not statistically significant and represent an experimental trend. The results indicate a possible orientation-dependent influence on size-resolved aerosol behavior, requiring further confirmation.